Constant term of the reduction by x^2->x+1 of the polynomial p(n,x) defined below in Comments.

Terms

a(0) =1a(1) =7a(2) =12a(3) =23a(4) =39a(5) =66a(6) =109a(7) =179a(8) =292a(9) =475a(10) =771a(11) =1250a(12) =2025a(13) =3279a(14) =5308a(15) =8591a(16) =13903a(17) =22498a(18) =36405a(19) =58907a(20) =95316a(21) =154227a(22) =249547a(23) =403778a(24) =653329a(25) =1057111a(26) =1710444a(27) =2767559a(28) =4478007a(29) =7245570